I have a concrete driveway that I'd like to keep looking good, and in good working order. What needs to be done to maintain the driveway, and how often should it be done?
Driveways should be cleaned on a somewhat regular basis (at least 2 times a year). If you have a power washer, use that, otherwise a hose with a strong stream will do it.
With a power washer, you can use driveway cleaning solutions to add a little soap into the mix. If you don't have a power washer, use a bucket and a stiff brush.
Obviously, not all driveways are created equally so this could be quite the project depending on how long and wide it is. Concrete is like any other porous material exposed to the elements; your looking to wash away salt, acid from rain, from car exhaust, from general traffic, etc...
Secondly, you'll want to repair any cracks in the concrete. Cracks in expansion joints can be filled in with a non-hardening UV safe silicon, while cracks in the actual driveway should be repaired with a concrete repair mortar.
In colder climates, water can get into cracks and when it freezes over winter, it can cause the concrete to shift, causing more damage.
If you choose to, you can use a concrete sealer; this is usually rolled on and seals the pours in the concrete to prevent water penetration and generally makes it easier to wash the concrete the next time around. You'll do this about once a year.
You can go a bit extreme and use a concrete epoxy with some aggregate (sand) mixed into it to further protect the concrete. This is usually used in a garage to provide an easy to maintain and clean work surface, but this can get expensive and is usually found in automotive shops.
Nothing. Put nothing on the concrete and keep anything from it and it will last a very long time. No salt, no power washing, no sealers (often seal for a certain amount of time but the chemicals put wear on concrete), no acidic washing (for oil spills or whatever), no oil if you can keep that from happening. Soap and water for messes. If you can, keep from shoveling/scraping it in the winter.
Also take notice to areas around the concrete, including spacing in-between pads. Keep them free of weeds and debris. Make sure tree roots don't find there way under - so watch when you are planting a young tree next to it. Also I have seen issues with concrete pads failing because of rodents - chipmunks, mice, rats, moles. Don't let them make a home under your pads - or your pads will dip where they built tunnels. Watch for any holes next to concrete pads. Last thing I would say is don't do stupid things - like I have seen people add an air condition unit on the edge of a poured patio... and wonder why that corner of the patio broke off or dipped after a couple years.
I noticed I answered this for a temperate or warmer climate. For a colder climate I would suggest a sealer - again you will have to see what the original sealer is - because you cannot just layer some sealers. You would seal every 5 years. Main thing is making sure you don't have a lot of expansion and contraction because of water freezing in the concrete. There are also sealers that keep salt residue out so that is a big thing in some climates/countries. In the US we use tons of salt comparatively and even if you don't salt your driveway your car might be.
No matter the climate I am very against power washing. I understand that you may need to every few years to make it look nice but I would really try a hose and soap.